This invention relates to the use of substantially water-insoluble silicic acid esters containing polypropylene glycol groups and, optionally, polyethylene glycol groups as foam inhibitors in foaming systems.
It is know that organopolysiloxanes, particularly in conjunction with silica aerogel, have foam-suppressing properties and, by virtue of those properties, are widely used as defoaming agents. However, their production is relatively complicated, so that there is an interest in more readily obtainable defoaming agents. In numerous fields of application, their strong hydrophobizing properties give rise to problems through undesirable surface effects. Their extremely high resistance to environmental influences can also be a disadvantage because, on the other hand, their foam suppressing properties are, in general, only briefly utilized, as for example in food production or papermaking, while on the other hand the period of time up to mineralization under environmental conditions is extremely long.
There has been no shortage of attempts to replace organopolysiloxanes by other substances having a comparable defoaming effect. In most cases, however, only partial solutions have been achieved, i.e. the substitutes only show a satisfactory effect in specific systems or in special applications, but frequently fail in the event of changes in the conditions under which they are used. Accordingly, there is still a considerable interest in universally useable foam inhibitors which are not attended by any of the disadvantages mentioned above.
On the other hand, silicic acid esters from compounds containing polyglycol ether groups are known. Orthosilicic acid esters of water-soluble, ethoxylated, relatively high-molecular-weight alcohols and alkyl phenols, which are suitable for use as pigment dispersants in aqueous media, are described in "Chemistry, Physics and Application of Surface Active Substances", Proc. Int. Congr. 4th 1964, Vol. 1 (1967), pages 199 to 207. There is no mention of any foam-inhibiting effect. Neither would such an effect be attributed to compounds such as these on account of their relatively high solubility in water. German No. 1,644,945 describes orthosilicic acid esters of polyethylene glycol and butyl polyethylene glycol and also their use as hydraulic oils. There is no reference to their use as form inhibitors. Finally, U.S. Pat. Nos. 3,935,133 and 4,097,406 describe reaction products of silicon tetrachloride with alcohols and partial replacement of the alcoholate with mono-lower alkyl ethers of ethylene oxide-propylene oxide block polymers which are used as stabilizers in the production of polyurethane foams. There is no indication in either of these two patents that compounds of this type have a foam-inhibiting effect.